Along with rapid market expansion of laptop computers, cell phones, electric cars, stationary power storage systems and the like, inexpensive, safe, long-life and high-energy density secondary batteries have been demanded. As candidate secondary batteries, lithium ion secondary batteries, which have a high energy density and no memory effect, are supposed to be one of prospective secondary batteries. Particularly in recent years, attention has been paid to the so-called self-discharge property in which the charge capacity does not reduce even when the batteries stand by as being in the charged state.
Means of providing inexpensive, safe, long-life and high-energy density secondary batteries include a method of using an inexpensive and safe lithium manganese composite oxide-based positive electrode, a method of using an inexpensive carbon-based negative electrode, and a method of using a nonaqueous electrolyte solution excellent in stability. Particularly technologies of using a nonaqueous electrolyte solution excellent in stability are important. The reason thereof will be described hereinafter.
In the charge and discharge process of a lithium ion secondary battery, the desorption and absorption reactions of lithium ions occur at the interface between an electrode and an electrolyte solution. At this time, other than these reactions, decomposition reactions of an electrolyte solution solvent and a supporting electrolyte salt may take place in some cases. The decomposition reaction forms a high-resistance film on the electrode surface, and inhibits the desorption and absorption reactions of lithium ions, which should occur primarily. It is known that as a result, the irreversible reduction of the discharge capacity, and the like are promoted and characteristics as a secondary battery degrade.
In order to suppress such degradation, various contrivances have been made. As one of them, a method of forming a protection film on the electrode surface to thereby suppress the above decomposition reaction is exemplified; and means therefor is proposed in which an electrolyte solution additive having a film forming ability is added to an electrolyte solution.
Based on the above, there are disclosed technologies of suppressing the degradation of secondary battery characteristics, particularly some technologies of improving the cycle characteristics and suppressing the internal resistance of a secondary battery in storage.
Patent Literature 1 discloses, as a method of improving the cycle characteristics in the case of using a lithium manganese composite oxide for a positive electrode, a technology in which an electrolyte solution contains a composition capable of reacting with water and generating hydrogen ions, and a hydrogen ion scavenger is disposed at a place in a battery of contacting with the electrolyte solution.
Patent Literature 2, Patent Literature 3 and Patent Literature 4 disclose, as methods of forming a protection film on the electrode surface to thereby suppress the decomposition reaction of an electrolyte solution, a technology in which a secondary battery electrolyte solution containing a cyclic sulfonic acid ester having at least two sulfonyl groups is used, and a technology in which a cyclic or chain disulfonic acid ester having an unsaturated bond is used.
Patent Literature 5 and Patent Literature 6 disclose a technology in which a lithium nickel composite oxide and chain and cyclic disulfonic acid compounds are contained. Patent Literature 7 describes a lithium ion secondary battery having an electrolyte solution containing a cyclic sulfonic acid ester.
Additionally, there have been made various proposals on other electrode materials, shapes, production conditions, and materials such as additives.